The present invention relates to a metal housing for electronic devices. The housing includes a housing body composed of housing parts that are connected with one another so as to be electrically conductive and leave at least one opening for access to the interior of the housing as well as a closing element for closing the opening and metal contact faces provided at the housing body around the opening and correspondingly at the closing element. These metal contact faces establish a highly electrically conductive connection with one another so as to seal the groove between the housing body and the closing element against interfering electromagnetic radiation. A housing of such a configuration is disclosed, for example, in the published, unexamined German Patent Application No. 3,815,517.
The present invention further relates to a method of producing such a housing.
The operation of electronic devices may be subject to interference from high frequency electromagnetic radiation. Devices employed in the high-frequency art may also themselves radiate electromagnetic waves and thus cause undesirable interference in their environment. To avoid such interferences, the electronic devices must be installed in housings that are tight against high frequencies. Ideally, the electronic devices to be shielded are encased in an uninterrupted sheath of an electrically conductive metal. The Faraday cage formed thereby ensures the desired electromagnetic compatibility (EMC).
However, one or more openings must be provided in the housing to assemble and service the electronic devices. These openings must be closed as tightly as possible by means of an appropriate closing element, for example a door or a flap. The unavoidable grooves between the housing body and the openable closing element adversely affect the shield against the penetration and radiation of electromagnetic waves into and out of the housing interior.
It is known in connection with housings properly constructed for EMC to specially seal the grooves between closing elements and housing body by means of additionally inserted elastic seals of an electrically highly conductive material. For this purpose, mutually corresponding metal contact faces must be provided around the opening in the housing body as well as at the pivotal or removable closing element. A suitable seal composed of an electrically conductive contact strip having resiliently yielding regions is disclosed in the published, unexamined German Patent Application No. 3,642,588. In some cases, such an additional HF seal may not be necessary if it is ensured in some other, for example structural, manner that the contact faces of the housing body and of the closing element lie cleanly against one another.
The electrical transfer resistances between the contact faces and between the contact faces and an inserted HF seal must be as low as possible to realize a high shielding effect for the housing. The higher the conductivity of the materials that are in contact with one another, the lower are the transfer resistances that can be realized. Moreover, it must be ensured that the contact faces remain free of corrosion over the entire service life of the housing.
The published, unexamined German Patent Application No. 3,725,929 discloses a method in which an electrically conductive layer as well as a magnetically permeable material is precipitated by wet chemical means on the surface of a nonmetallic housing - preferably a plastic housing.
German Utility Model Patent No. 86/24,817.0 further discloses a structure composed of a thin polyester sheet as the carrier and a laminated-on aluminum foil as a shield for electronic components.
It is known that EMC housings can also be constructed of aluminum sheets having a bare surface or of stainless steel. If, however, as is generally the custom for reasons of economy, steel sheet is employed, its surface must be provided with a corrosion resistant layer before it is processed. Often HF-tight electronic housings are produced of steel sheet whose surface has been coated with zinc. However, pre-zinced sheets cannot always be processed, for example whenever weld connections ar required to produce the housing. In those cases, a zinc layer must subsequently be additionally applied galvanically, at least in the region of the desired contact faces. Particularly if the housings or housing components have larger dimensions, subsequent zincplating is connected with considerable expenditures.
The use of steel sheets coated with nobler metals than zinc has not been taken into consideration in the past for reasons of cost and also because it would then be difficult to perform the bending and welding processes.